A. Field of Invention
The present invention pertains generally to scanners and more particularly to enhancing the resolution of scan data.
B. Description of the Background
A common method of generating an image of an object is to scan the object with detectors and generate a display of the scanned information. Detectors that detect specific spectral bands can be used to generate a color image. For example, if detectors are used that are capable of scanning the spectral bands of three primary colors, a full natural color image can be generated of the object. Additionally, other spectral bands such as the infrared band or the ultraviolet band may also be useful for certain applications. In addition, images from various spectral bands can be combined to produce a wide variety of images.
The speed at which an object is scanned is determined by a wide variety of factors such as movement or change in the object, limitations relating to the mechanics of the system used for scanning, the exposure period of the detectors, the energy of the radiation being detected, etc. For example, space satellites move at various speeds with respect to the surface of the earth that define the scanning speed at which detectors and optics mounted in the space satellite are able to scan a predetermined area on the earth's surface. Consequently, exposure of the detectors must be sufficiently fast to match the speed at which the object is being scanned. As another example, it is desirable to have a document scanner, such as a flatbed document scanner, a copier, a fax machine, or any other type of scanner that scans documents, to scan the document as quickly as possible. In this case, the shorter the exposure period of the detector, the faster the document can be scanned.
To obtain a shorter exposure period for a detector, such as a charged coupled device (CCD), the size of the detector can be increased to capture more photons in a shorter period of time. However, increasing the size of each individual element of a detector such as a CCD linear array, decreases the resolution of the signal that can be obtained. Since fewer detector elements can be utilized, this problem can be further exacerbated by the fact that the detection of specific spectral bands of radiation reflected from an object normally limits the number of electrons that are sensed by the detector. For some energy bands of radiation, the sensitivity of each element of the CCD array may also be less which requires that each element of the array must be further increased in size. On the other hand, panchromatic detectors, i.e., black and white detectors that detect a wide spectral band of radiation, sense a much greater number of photons which allows the size of each of the panchromatic detector elements to be significantly decreased while maintaining the same exposure period. Hence, panchromatic detectors are capable of having a much higher resolution than detectors that detect only a narrow spectral band.
For high scanning speeds, such as in space-based detectors, aircraft-based detectors, etc., panchromatic detectors are capable of producing a much higher resolution signal than detectors that sense a narrow spectral band because the panchromatic detector elements can be made smaller. For document detectors, a desired resolution can be obtained at a much higher scanning speed with a panchromatic detector, than a detector that is designed to sense a spectral band for a primary color.
It would therefore be desirable to increase the resolution of the image data from detectors that detect a specific spectral band, which are collectively referred to herein as multi-spectral detectors that generate multi-spectral image data. Specifically, it would be desirable to increase the resolution of the multispectral detectors to a resolution that is equivalent to panchromatic detectors, that generate panchromatic image data. It is against this background and these problems and limitations that the present invention has been developed.